This invention relates to improvements in a PCM recording and reproducing system and more particularly to means for smoothing the noise from the loss of digital signals that may occur resulting from the splice editing of a PCM magnetic record tape.
PCM recording and reproducing systems are already well known in the field of the digital recording technique. Among them, PCM recording and reproducing systems utilizing magnetic record tape and including multi-track type stationary recording and reproducing heads are advantageous in that the mechanism is not only simple but also splice editing is possible. Particularly, PCM recording and reproducing systems for sound signals indispensably require editing of the magnetic record tape and are especially advantageous in that the splice editing can be performed with a single recorder.
Splice editing involves cutting the magnetic record tape in order to remove an unnecessary portion thereof or to insert a required tape portion and splicing the tape portions into a single tape by applying short lengths of a splicing tape to the tape portions to be joined. However, upon reproducing digital signals recorded on the spliced tape portion, some of them will be lost for the following reasons. The cutting of the magnetic record tape causes the deterioration of the record on that portion of the tape adjacent to the cut end thereof. When the cut end portions of the tape are spliced to each other, the splice angle with the longitudinal axis of the tape may deviate from a predetermined splice angle, a mismatch may occur in the joint of the tape portions, the splicing tape may extend and so on. Also during the travel of the tape the spliced portion thereof may touch the associated head in a manner ineffective for good recording or reproduction. Even with splice editing effected by using a jig, it is impossible to fully eliminate this loss of the digital signals. The manual splice usually utilized results in the loss of the reproduced signal for a few milliseconds. This means that several thousand bits will be lost assuming that the recording speed is on the order of 1 megabits per second. This figure is very large as compared with scores of bits usually lost resulting from flaws and scratches on and dust adhering to the magnetic record tape. Therefore conventional compensation methods for the loss of reproduced signals are not effective. As a result, conventional PCM recording and reproducing systems have been disadvantageous in that noise is generated upon converting a reproduced digital signal to the original analog signal and the resulting signal quality is much impaired particularly for sound signals.
Accordingly, it is an object of the present invention to provide a new and improved PCM recording and reproducing system free from the noise of reproduced digital signals due to the splice editing of the PCM record medium by smoothing the loss of digital signals lost upon reproduction of the spliced tape portion with other digital signals stored in a memory and reproduced with a predetermined delay time.
It is another object of the present invention to provide a new and improved PCM recording and reproducing system for continuously reproducing an output signal from the PCM record medium involved by smoothing the noise from the loss of reproduced signals resulting from the splice editing of the PCM record medium.
It is still another object of the present invention to effectively perform the splice editing of PCM magnetic record tapes.